1. Field of Invention
The present invention relates to a motor vehicle headlamp having a multi-function projection module.
2. Description of the Related Art
A multi-function projection module involves a projection module by means of which it is possible to switch between different light functions. Examples for such light functions are low beam functions and high beam function.
A headlamp of this type is known from the JP 2006107875 and from the DE 10 2009 049 458 A1. This well-known headlamp has a bi-function projection module which comprises a first light source, a primary lens system, a second light source, a second primary lens system, an aperture having an aperture edge, a projection lens and a mirror. The headlamp converts light from the first light source into a first light distribution located in the front end of the projection module by means of the first primary lens system in a first beam-path bounded by the aperture edge. It has also been designed to focus light of the second light source into a beam waist by means of the second primary lens system in a second beam-path and to convert said light into a second light distribution located in the front end of the projection module, the second light distribution having a predetermined central point. The beam waist involves the strongest contraction of the high beam beam-path, i.e., the waist of the high beam bundle of rays.
Contrary to a reflection module in which a reflector collects the light of a light source and reflects it in a desired light distribution, a projection module is generally characterized in that it reproduces a light distribution generated inside the headlamp by means of a projection lens in a light distribution located in the front end of the headlamp. The light distribution generated inside the headlamp can comprise the light distribution in a light-emitting surface of a light source. However, in most cases such light distribution comprises a light distribution which is generated as an intermediate image in the focal plane by a primary lens system and an aperture.
For switching between a low beam distribution and the high beam distribution in most cases the position of the aperture is changed with regard to the light distribution generated in the headlamp. The position change takes place by means of a motorized drive of the aperture. At the same time, the different light distributions are generated by specifically blocking light beams which usually originate from a particular light source. The only light source is usually a gas discharge lamp.
Currently there are headlamps available that generate, for instance by means of projection lenses, from the light of several semi-conductor sources low beam or high beam distributions. Subsequently, such headlamps are described also as LED headlamps. Contrary to headlamps provided with gas discharge lamps as light sources, subsequently described also as Xenon headlamps, LED headlamps usually require not only several light sources, i.e., LED chips, but also a plurality of associated projection or reflection lenses. As a result, the total light distribution of LED headlamps is generally formed through superimposed light distributions of a plurality of light modules.
Efforts are now made to use the flexible apertures inserted in Xenon headlamps also in LED projection modules in order to be able to fulfill several low beam and/or high beam functions with a single light module. To this end, the low beam distribution is generated by blocking a portion of the high beam distribution. However, because of the low performance of the LED light modules, the required blockage of greater streams of light is particularly disadvantageous.
These disadvantages are avoided when the beam-paths for the respective light functions in the aperture plane of the projection module are divided so that the bundles of rays assigned to the light functions can be generated from different light sources that can be independently switched. As a result, it is possible to reproduce several light functions without using flexible apertures. At the same time, the different light functions are switched by merely switching the light sources on and off.
Depending on the physical effect, the division of the beam-path can be achieved by means of refraction, reflection or absorption. In this context, it is known from the DE 10 2007 052 696 A1 that a high beam and a low beam beam-path can be formed by means of internal total reflection on a boundary surface of a glass body, the edge of which generates a cut-off line in the low beam direction of the light. At the same time, the high beam bundles of rays are coupled into the same glass body as the low beam bundles of rays but impact the above-mentioned boundary surface at considerably steeper angles. As a result, they are not reflected but penetrate the surface and illuminate the area above the cut-off line and thus form a high beam distribution.
From the DE 10 2009 008 631 A1 it is known to guide a beam-path through a glass body having an integrally molded mirror surface where internal total reflection occurs. The beam-path is restricted by the fully reflecting surface in the focal plane of the projection lens in such a way that a strong cut-off line (HDG) is generated. Additional beam-paths are guided past the glass body in order to implement high beam functions.
When using mirror shutters according to the DE 10 2007 052 696 A1 or according to the DE 10 2009 008 631 A1 which operates in accordance with the total reflection method, it has to be ensured that the largest possible amount of beams coupling into the glass body leave the glass body in a controlled manner via the light emission surface on the front end. Moreover, the lowest amount of beams should escape on the side surfaces of the glass body because such beams could result in undesired stray light and/or glare.
Furthermore, it has to be ensured that only a small proportion of the beam-path to be guided past the glass body impacts the glass body and is there coupled into the glass body through refraction occurring perpendicular to the boundary surface at the impact point of the beam. These beams are lost for the desired light distribution because usually they no longer leave the glass body.
The US 2006/0120094 A1 and the DE 10 2008 036 192 A1 describe an alternative approach of using internal total reflections: here the beam-path is divided above and below the cut-off line by two reflecting surfaces and is projected onto the road through the lens of the projection module. This system can be designed also with absorbing surfaces which would, however, result in efficiency losses when compared with the model having reflecting surfaces.
These systems involve a difficulty with regard to producing a cut-off line in the desired light distribution. The difficulty consists of dividing the beam-paths of the different light functions in such a way that in the low beam function no undesired light is scattered beyond the cut-off line (no crosstalk), and in the high beam function no dark or colored line remains at the place of the low beam cut-off line.
In the subject matter of the above-mentioned JP 2006107875, these problems are avoided in that a high beam beam-path is guided through the projection lens past the aperture of the low beam beam-path.
However, since the associated high beam distribution would appear far above the horizon, a mirror is used in the subject matter of the JP 2006107875, the mirror being arranged in the optical path behind the projection lens, directing the high beam downward. However, from the aspect of design, such a mirror is often considered to be disturbing.